In one known application such a pump comprises a thrust collar on a driving shaft, whose external cylindrical surface moves in close co-operation with an internal cylindrical surface of a surrounding stator ring in which the channel is formed. Viscous drag enables the rotor to pull the fluid from the channel and to pressurise it.
The collar may be a collar provided as a shaft to co-operate with thrust pads to carry shaft thrust loads. Since such pads require forced lubrication, a viscosity pump may be eminently suitable for providing that lubrication, and indeed may also provide auxiliary lubrication for the motor driving the shaft.
Difficulties with viscosity pumps are that there can be an unacceptable amount of wear between co-operating surfaces of the stator and rotor other than at the channel with consequent leakage and also that priming of the pump at starting is not easy, and wear may occur before the pump has been fully primed.
It is an object of the present invention to overcome these disadvantages.